Air pressure - density -temperature at 10,000 meters

AI Thread Summary
At an altitude of 10,000 meters, the air temperature is approximately -35º C, while cabin temperatures in airplanes remain comfortable due to air conditioning. The discussion revolves around calculating the air pressure and temperature at this altitude, noting that the provided air density of 1.29 kg/m3 is inaccurate for higher altitudes. Participants suggest using the ideal gas equation and external resources to determine the correct pressure and density. The challenge lies in the lack of information about how much the air conditioner cools the air, complicating the calculations. Ultimately, accurate values for pressure and temperature must be derived from atmospheric data and the ideal gas law.
Sherry
Messages
7
Reaction score
0
The air temperature at an altitude of 10,000 meters is a chilling
-35º C. Cabin temperatures in airplanes flying at this altitude are comfortable because of air conditioners rather than heaters. A.) Find the pressure at 10,000 m and B) Find the temperature of the air before the air conditioner cools it off.
 
Science news on Phys.org
Ideal gas equation (not enough information is given though - some big assumptions need to be made).
 
This was a question the teacher gave us to think about over the weekend.

The only clue he gave us in class is:
101325 Pa = (1.29 kg/m3)(h) where h = 8015 meters.

He told us to use air density 1.29 kg/m3 but that does not make sense because dry air at sea level is 1.29 kg/m3 but as altitude increases, the density drops dramatically.


I found other formulas and worked the problem this way:

Where: D = density, kg/m3
P = pressure, Pascals
R = gas constant , J/(kg*degK) = 287.05 for dry air
T = temperature, degK = deg C + 273.15


D = P/R*T D = 26436/(287.05 * 238) D = 0.38696 kg/m3
P = 101325-egh P = 101325-(0.38696)(9.80)(10000) P = 63403 Pa
P = Po(Tf/To) 101325 = 63403(Tf /238) Tf = 380 K = 107 C

I am just not sure that it is right.
 
Last edited:
Originally posted by Sherry
He told us to use air density 1.29 kg/m3 but that does not make sense because dry air at sea level is 1.29 kg/m3 but as altitude increases, the density drops dramatically.

But not inside a pressurised airliner. I believe that is the key to resolving this question.
 
Correct, but he wants us to find the pressure outside of the plane at 10,000 meters as well as the temperature of the air as it is being pressurized but before the plane's air conditioner cools it off.
 
You can't calculate the air pressure outside the plane from the info given because you don't know how much the air conditioner has cooled the air. Find the pressure and density through http://www.npl.co.uk/pressure/faqs/atmosaltitude.html chart (if it isn't specific enough, calculate it by fitting a line to the graph) and calculate the temperature of the air once its been pressurized using the ideal gas equation.
 
Thread 'Thermo Hydrodynamic Effect'
Vídeo: The footage was filmed in real time. The rotor takes advantage of the thermal agitation of the water. The agitation is uniform, so the resultant is zero. When the aluminum cylinders containing frozen water are immersed in the water, about 30% of their surface is in contact with the water, and the rest is thermally insulated by styrofoam. This creates an imbalance in the agitation: the cold side of the water "shrinks," so that the hot side pushes the cylinders toward the cold...
Back
Top